Hydrogen generation

ABSTRACT

An apparatus and method including storage and dispensing vessels to safely store and dispense gaseous hydrides, where the storage and dispensing vessels contain a solid-phase physical sorbent medium having a physically sorptive affinity for gaseous hydrides, and wherein the gaseous hydride is decomposed in the apparatus to generate hydrogen gas. The gaseous hydrides include, but are not limited to, silane, germane, stibine and diborane. The gaseous hydrides decompose spontaneously and/or decomposition is enhanced using surface modified adsorbents. The hydrogen generated by the apparatus may be used in a fuel cell or other hydrogen gas consuming unit.

FIELD OF THE INVENTION

The instant invention relates generally and specifically to solving theproblem of insufficient hydrogen storage capacity in a vessel or tank,while simultaneously permitting the safe and efficient generation ofhydrogen fuel. Specifically, this invention relates to an apparatus andmethod using storage and dispensing vessels that safely store anddispense gaseous hydrides wherein the gaseous hydride is decomposed inthe apparatus to generate hydrogen gas.

BACKGROUND OF THE INVENTION

As the world's population expands, so does the use of carbon-based fuelswith a concomitant increase in the amount of carbon dioxide releasedinto the atmosphere. Most now accept that the ever-increasing cumulativeamount of atmospheric carbon dioxide is warming the earth's atmosphere,causing climate change. Within the last twenty-five years, there hasbeen a recognition that the global energy system must move steadily awayfrom a reliance on carbon-rich fuels whose combustion products includethe greenhouse gas carbon dioxide. Furthermore, the extraction andmovement of fossil fuels around the globe exacerbates global pollutionand is a causative factor in the strategic military struggles betweennations.

During the latter portion of the 20^(th) century, combustible fuelalternatives, including natural gas and hydrogen, gained prominence asbeing environmentally cleaner alternatives to higher-carbon based fuelssuch as oil. This trend towards lower-carbon fuels, combined with thegreater energy efficiency of the modern engines has significantlyreduced the amount of carbon released into the atmosphere per combustionunit However, further decreases in carbon released into the atmosphereare necessary to stave off future catastrophes caused by a runawaygreenhouse effect

Hydrogen is the “ultimate fuel.” While the world's oil reserves aredepletable, the supply of hydrogen remains virtually unlimited. Hydrogencan be produced from coal, natural gas and other hydrocarbons. Hydrogencan also be produced without the use of fossil fuels, such as by theelectrolysis of water using alternative energy sources (e.g.,hydroelectric, wind, solar, geothermal, etc.). Furthermore, hydrogen,although presently more expensive than petroleum, is an inherently lowcost fuel. Hydrogen has the highest density of energy per unit weight ofany chemical fuel and is essentially non-polluting since the mainby-product of the oxidation of hydrogen is water. Thus, hydrogen can bea means of solving many of the world's energy related collateralproblems, such as climate change, pollution, and a strategic dependencyon oil.

To date, the greatest challenge is undoubtedly the need for acost-effective, on-board hydrogen storage system that will meet the DOEminimum vehicle range of 300 miles within the weight and volumeconstraints of the vehicle. DOE emphasizes that this is the greatestchallenge, since no hydrogen storage technology available today can meetthe DOE cost and performance targets even in light of the well-developedhydrogen production and fuel cell technologies (Farrauto, R., ACSDivision of Fuel Chemistry, 226^(th) ACS National Meeting, New York,September 2003, paper No. 87, “Catalysts for the Hydrogen Economy”).Although hydrogen can be stored in several ways, e.g., on a solidadsorbent, as a cryogenic liquid, as a compressed gas, or even as asolid chemical hydride, significant barriers must be overcome with eachof these methods before the targeted goals can be achieved.

For example, storage of hydrogen as a compressed gas involves the use oflarge and heavy vessels. In a steel tank of common design at a typicalpressure of 136 atmospheres, only about 1% of the total weight is thatof the hydrogen gas. This is unacceptable knowing that almost 23 molesof hydrogen gas must be oxidized to release as much energy as thecombustion of 1 mole of octane. Storage of hydrogen as a liquid also hasdisadvantages because liquid hydrogen must be kept extremely cold (below−253° C.) and is highly volatile if spilled. Moreover, liquid hydrogenis energetically expensive to liquefy and maintain in the liquefiedstate. For example, the losses associated with hydrogen evaporation canbe as high as 5% per day. Whether stored as a liquid or gas, hydrogenstorage is highly dangerous due to the flammability of the gas.

Various other storage approaches have been tried—adsorption of H₂ oninert solids, storing liquid petroleum or methanol followed by reformingto H₂, and decomposition of solid hydrides to form H₂. Conventionaladsorption methods and materials have been shown to be completelyinadequate. Although reports in 1997 of high hydrogen adsorption levelson carbon nanotube adsorbents was thought to solve the storage problems(Dillon, A. C., Jones, K M., Bekkedabl, T. A., Kiang, C. H., Bethune, D.S., Heben, M. J., “Storage of Hydrogen in Single-walled CarbonNanotubes,” Nature (London), 386(6623), 377-379 (1997); Chambers, A.,Park, C., Baker, R. T. K., Rodriguez, N. M., “Hydrogen Storage inGraphite Nanofibers,” J. Phys. Chem., 102(22), 42534256 (1998); and U.S.Pat. No. 5,653,951 in the name of Rodriguez, et al. issued Aug. 5,1997), attempts to recreate the reported work have been disappointing(Dagani, R., “Tempest in a Tiny Tube,” Chem. & Eng. News, Jan. 14, 2002,p. 25, and Tibbetts, G. G., Meisner, G. P., Olk, C. H., “HydrogenStorage Capacity of Carbon Nanotubes, Filaments and Vapor-Grown Fibers,”Carbon, 39(15), 2291 (2001)). McEnaney reviewed the state of the art ina review paper in 2003 and concluded that numerous claims had been made,but there was little convincing evidence that hydrogen could be adsorbedat the levels required (McEnaney, B., “Go Further with H₂ ,” Chem. inBritain, 39(1), 24 (2003)).

Hydrogen can be stored as a chemically-bonded metal hydride, and muchwork is underway to demonstrate such technology. This work centers onthe use of hydrogen storage alloy materials (see, e.g., U.S. Pat. Nos.6,746,645, 6,491,866 and 6,193,929 in the name of Ovshinsky et al.). Inpractice, H₂ is physisorbed onto the storage alloy, separates intoatomic hydrogen, and bonds with the metal alloy forming metal hydride.To release the hydrogen from the metal hydride, the metal hydride isheated. These technologies, while promising, introduce other challenges,such as poor gravimetric energy density of the fuel (McEnaney, B., “GoFurther with H₂ ,” Chem. in Britain, 39(1), 24 (2003)), and the factthat the solid hydrides must be heated to relatively high temperaturesin order to release hydrogen.

The military has identified the need for small portable electric powersupplies. The U.S. infantryman, for example, has become extremelyefficient through the use of high tech devices; e.g. devices whichprovide him with communication and night vision capabilities. However,these devices require increasing amounts of portable electric power.Currently available battery packs are heavy and unwieldy and functionfor only a few hours at a time before requiring recharge. Re-chargingdevices using fuel cells are under development but these requirehydrogen fuel, supplied either from a compressed gas cylinder or moreusually, by catalytic treatment of a liquid fuel such as methanol. Onedownside to the use of methanol is that the catalytic treatment processuses some of the produced hydrogen fuel to convert methanol to hydrogenfuel, which is highly inefficient. However, because it is unfavorable totransport heavy, high pressure compressed hydrogen gas cylinders,methanol is still the re-generator of choice.

U.S. Pat. No. 5,518,528 issued May 21, 1996 in the names of Glenn M. Tomand James V. McManus, describes a gas storage and dispensing system, forthe storage and dispensing of gases, which comprises anadsorption-desorption apparatus, for storage and dispensing of a gas,e.g., a hydride gas. The gas storage and dispensing vessel of the Tom etal. patent reduces the pressure of stored sorbate gases by reversiblyadsorbing them onto a carrier sorbent medium such as a zeolite oractivated carbon material.

More specifically, such storage and dispensing system comprises: astorage and dispensing vessel constructed and arranged for holding asolid-phase physical sorbent medium, and for selectively flowing gasinto and out of said vessel; a solid-phase physical sorbent mediumdisposed in said storage and dispensing vessel at an interior gaspressure; a sorbate gas physically adsorbed on the solid-phase physicalsorbent medium; and a dispensing assembly coupled in gas flowcommunication with the storage and dispensing vessel.

The storage and dispensing vessel of the Tom et al. patent thus embodiesa substantial advance in the art, relative to the prior art use ofhigh-pressure gas cylinders. Conventional high pressure gas cylindersare susceptible to leakage from damaged or malfunctioning regulatorassemblies, as well as to rupture or other unwanted bulk release of gasfrom the cylinder if internal decomposition of the gas leads to rapidincreasing interior gas pressure in the cylinder.

It would therefore be a significant advance in the art of hydrogenstorage to provide an improved storage and dispensing apparatus anddecomposition method based on the storage and dispensing vessel of Tomet al., which can adsorb substantial quantities of gaseous hydride andcan safely and easily be used without risk to the user.

Other objects and advantages of the invention will be more fullyapparent from the ensuing disclosure and appended claims.

SUMMARY OF THE INVENTION

The present invention relates generally to the storage and dispensing ofgaseous hydride species and the decomposition of the gaseous hydridespecies to generate hydrogen gas.

In one aspect, the present invention relates to an apparatus for storingand dispensing a sorbate gas, wherein the sorbate gas undergoesdecomposition to form hydrogen gas, said apparatus comprising:

-   -   (a) a storage and dispensing vessel containing the sorbate gas        in a physically adsorbed state; and    -   (b) a decomposition chamber, said decomposition chamber        comprising a decomposition portion and a collection portion,        wherein the storage and dispensing vessel is communicatively        connected to the decomposition portion, and wherein the        decomposition portion and the collection portion are separated        by a gas permeable membrane.

In another aspect, the present invention relates to an apparatus forstoring, dispensing and regenerating a sorbate gas, said apparatuscomprising:

-   -   (a) a storage and dispensing vessel containing the sorbate gas        in a physically adsorbed state;    -   (b) a decomposition chamber, said decomposition chamber        comprising a decomposition portion and a collection portion        separated by a gas permeable membrane, said decomposition        portion having a modified surface adsorbent disposed therein,        wherein the storage and dispensing vessel is communicatively        connected to the decomposition portion of the decomposition        chamber, and wherein the sorbate gas undergoes decomposition in        the decomposition chamber to form a metal and hydrogen gas        therein; and    -   (c) a hydrogen-containing source communicatively connected to        the collection portion of the decomposition chamber.

In yet another aspect, the present invention relates to an apparatus forstoring and dispensing a sorbate gas, said apparatus comprising astorage and dispensing vessel containing the sorbate gas, said storageand dispensing vessel comprising:

-   -   (a) a vessel constructed and arranged for holding a solid-phase        physical sorbent medium;    -   (b) a solid-phase physical sorbent medium disposed in said        vessel at an interior gas pressure;    -   (c) a sorbate gas physically adsorbed on said solid-phase        physical sorbent medium; and    -   (d) a dispensing assembly coupled in gas flow communication with        the vessel and selectively actuatable for gas dispensing,        wherein the dispensing assembly comprises a gas permeable        membrane within the vessel,    -   wherein at least a portion of the sorbate gas undergoes        decomposition in the vessel to form hydrogen gas, and hydrogen        gas egresses the vessel through the gas permeable membrane of        the dispensing assembly during said gas dispensing.

In a further aspect, the present invention relates to a method forgenerating hydrogen gas by the decomposition of a sorbate gas, saidmethod comprising:

-   -   (a) desorbing at least a portion of said sorbate gas from a        solid-phase physical sorbent medium disposed in a storage and        dispensing vessel, said storage and dispensing vessel comprising        a solid-phase physical sorbent medium having a physically        sorptive affinity for said sorbate gas disposed therein;    -   (b) flowing the sorbate gas from the storage and dispensing        vessel to a decomposition chamber, and    -   (c) decomposing the sorbate gas in the decomposition chamber to        generate hydrogen gas.

In a still further aspect, the present invention relates to a method forgenerating hydrogen gas by the decomposition of a sorbate gas, saidmethod comprising:

-   -   (a) physically adsorbing a sorbate gas into a solid-phase        physical sorbent medium having sorptive affinity for said        sorbate gas, wherein the solid-phase physical sorbent medium is        disposed in a storage and dispensing vessel comprising a        dispensing assembly;    -   (b) decomposing at least a portion of said sorbate gas        physically adsorbed into the solid-phase physical sorbent medium        to form hydrogen; and    -   (c) flowing the hydrogen gas from the storage and dispensing        vessel to a hydrogen gas consuming unit.

Other aspects, features and embodiments of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Schematic cross-portional elevation view of the Wang et al.fluid storage and dispensing system.

FIG. 2A: Schematic of an embodiment of the gaseous hydride storage anddecomposition system disclosed herein.

FIG. 2B: Schematic of an embodiment for regenerating the gaseous hydridestorage and dispensing vessel as disclosed herein.

FIG. 3: Silane decomposition to hydrogen gas and silicon solid onuntreated carbon (various tests) and H₃PO₄-treated carbon.

FIG. 4: Silane adsorption/desorption isotherms at 294.2K

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF

The instant invention resolves the problem of insufficient hydrogenstorage capacity in a vessel or tank, while simultaneously permittingthe safe and efficient generation of hydrogen fuel. Specifically, thisinvention relates to an apparatus and method using storage anddispensing vessels that safely store and dispense gaseous hydrides, andin which the gaseous hydride is decomposed to generate hydrogen gas.

U.S. Pat. No. 5,528,518, issued May 21, 1996 in the names of Glenn M.Tom and James V. McManus, and U.S. Pat. No. 6,089,027, issued Jul. 18,2000 in the names of Luping Wang and Glenn M. Tom, are herebyincorporated by reference herein in their entireties.

The invention provides an alternative to conventional hydrogen storagemethods. The invention embodies the following operational aspects:

-   -   A. Safe storage of a gaseous hydride material in a reduced        pressure vessel; and    -   B. Decomposition of the gaseous hydride in order to generate H₂        according to the following general reaction:        M _(x) H _(y)(g)→xM(s)+y/2H ₂    -   where M includes, but is not limited to, Si, Ge, Sb or B; and        optionally,    -   C. An ability to regenerate (in situ or ex situ) the metal        product M, back to the gas hydride M_(x)H_(y) for storage in a        reduced pressure vessel.

These aspects are described individually in detail hereinbelow.

Safe Gaseous Hydride Storage

Many hydride gases, including silane, germane, stibine and diborane, arehighly toxic, posing environmental and human safety hazards. Therefore,a major barrier for accepting the concept of in situ generation ofhydrogen using a gas hydride precursor are concerns over accidental highpressure gas release of the toxic gaseous hydrides. Towards that end,Advanced Technology Materials, Inc. (Danbury, Conn.) developed andpatented the Safe Delivery System (SDS®), which includes a leak-tightgas vessel, such as a gas cylinder, containing the gas to be dispensed,e.g., silane, adsorbed into a sorbent material such as zeolite or othersuitable physical adsorbent material (see, Tom et al., U.S. Pat. No.5,518,528, which is incorporated by reference herein in the entirety).

Extensive investigations have demonstrated the value and safety of theSDS® gas vessel. For example, a conventional phosphine cylinder valvelocated in a secure cabinet was remotely opened and the maximum gasevolution rate measured during the release period. The release rate ofphosphine from the conventional high pressure cylinder attained levelsas high as 29,000 ppm/minute. An analogous experiment using an SDS®cylinder containing phosphine resulted in a maximum release rate of only480 ppb/minute. These tests and nearly ten years of perfectly safeperformance have convinced the semiconductor industry that these gasescan be handled safely in a routine manner. As many as 40,000 SDS®cylinders are currently in use worldwide.

In addition to the aforementioned safety advantages of storing gases inthe adsorbed phase, it has been recently discovered that the risk ofdeflagration can be reduced when storing deflagration-prone gases, suchas germane, in SDS® cylinders (see, U.S. Pat. No. 6,716,271 in the nameof Arno et al., issued Apr. 6, 2004, which is incorporated by referenceherein in the entirety).

The novel means and method of the present invention for storing anddelivering gaseous hydrides, e.g., germane, stibine, silane, phosphine,arsine and diborane, greatly reduces the hazard posed by these gases.The technique involves the adsorption of these gases into a physicaladsorbent such as, for example, zeolite 5A. By adsorbing the gas into azeolite or other suitable solid physical sorbent, the vapor pressure ofthe gas can be reduced to approximately 0 psig. The release potentialfrom this system is greatly reduced because the driving force ofpressure has been eliminated. Collectively, the storage and deliverysystem may usefully consist of a standard gas cylinder, loaded withsolid-phase adsorbent material such as zeolite, and a gas dispensingmechanism including a cylinder valve.

Zeolites are microporous crystalline aluminosilicates of alkali oralkaline earth elements represented by the following stoichiometry:M_(x/n)[(AlO₂)_(x)(SiO₂)_(y)]_(z)H₂Owhere x and y are integers with y/x≧1, n is the valence of the cation Mand z is the number of water molecules in each unit cell. Zeolite 5A hasapproximately 2.5×10²¹ hydride adsorption sites per gram. For example, aliter of zeolite will adsorb 100 grams of phosphine and 220 grams ofarsine at 25° C. and 1 atmosphere.

A particularly preferred solid-phase physical sorbent medium has a poresize in the range of from about 4 to about 13 Å. Examples of suchcomposition include 5A molecular sieves, and preferably a binderlessmolecular sieve. Other solid-phase physical sorbent mediums includecrystalline aluminosilicates, carbon molecular sieves, silica, alumina,macroreticulate polymers, kieselguhr, carbon, etc. For example, a literof carbon will adsorb 140 g of silane at atmospheric pressure. Thecharacteristics of the adsorbent used may be readily determined by oneskilled in the art. For example, the pore size distribution of theadsorbent may be optimized to yield optimum storage and desorptionrates. In addition, the adsorbent media may be pelletized, beaded, or asolid monolith block. The adsorbent may alternatively be channelized(see Tom et al., U.S. Pat. No. 6,764,755 issued Jul. 20, 2004, which isincorporated by reference herein in the entirety).

Because of the “unstable” nature of some of the hydrides, adsorbents mayneed to be passivated to prevent premature or uncontrolled decompositionduring storage. For example, boric acid treatment is a well-known methodfor oxidation suppression in carbon materials (McKee, D. W., Spiro, C.L., Lamby, E. J., “The Effects of Boron Additives on the OxidationBehavior of Carbons,” Carbon, 22(6), 507 (1984)), where it is believedto involve bonding of the (BO₃)_(n) chain to the carbon sites of the {101l} face of graphite.

Alternatively, the surface of the adsorbent may be modified prior tointroduction of the adsorbent into the storage and dispensing vessel toenhance decomposition. With regards to surface modification, it isbelieved that the passivating effect, i.e., the passivation of theadsorbent in the storage vessel to prevent premature or uncontrolleddecomposition during storage, observed in our own data is good evidencefor the importance of carbon edge-site chemistry in gaseous hydridedecomposition. Specifically, the development of higher-ratedecomposition catalysts produced by increasing the number of carbonsorbent active edge sites is proposed. Empirical determinations show theoccurrence of enhanced decomposition rates after doping the carbonsorbent material with phosphoric acid, implying a synergistic mechanisminvolving carbon edge sites and phosphorous. This enhanced decompositionby a phosphorus-containing compound was unexpected in view of McKee etal., who previously reported that graphite oxidation was inhibited byphosphorus additives (McKee, D. W., Spiro, C. L., Lamby, E. J., “TheInhibition of Graphite Oxidation by Phosphorus Additives,” Carbon,22(3), 285-290 (1984)). By systematically manipulating both edge-siteconcentration and the type, amount, and dispersion of inorganic dopantsin the carbon sorbent, an effective catalyst formulation for rapid,on-demand hydrogen production from the gaseous hydride source may beobtained.

For example, FIG. 3 illustrates the decomposition of silane as afunction of carbon site functionalization, as originally performedduring a study of undesirable decomposition during storage. It can beseen that the carbon sorbent doped with the H₃PO₄ material (+) greatlyenhances the decomposition of silane relative to undoped carbonsorbents. After six days, the volume of hydrogen produced during thedecomposition of silane in the presence of H₃PO₄-doped carbon sorbentwas 50% greater than the volume of hydrogen produced in the presence ofundoped carbon sorbent.

Importantly, the decomposition of gaseous hydrides may be eithersuppressed or enhanced depending on which doping agent is applied to thecarbon sorbent material prior to gaseous hydride loading. For example,boric acid doping of the carbon sorbent material reduces the rate ofdecomposition while phosphoric acid doping of the same sorbent doublesthe rate of hydrogen gas production relative to that of un-doped carbonsorbent. Thus, “surface modified adsorbent” as used herein can representthe enhancement or suppression of gaseous hydride decomposition in thepresence of doped sorbent material, depending on the particular dopantused.

In addition to the safety advantages, the storage technology of the SDS®vessel allows for a greater quantity of delivered gas. Approximately5-20 times more gaseous hydride may be stored in the SDS® vesselrelative to conventional high pressure cylinders. Since more gaseoushydride is delivered by the storage and delivery system, fewer cylinderchanges are required. Since most accidents with gases occur duringcylinder changes, safety is further improved.

Typically, the solid-phase physical sorbent medium chosen reduces thevapor pressure of the gaseous hydride to ≦1 atmosphere, and the vapor isselectively dispensed by pressure differential desorption of at least aportion of the sorbate gas from the sorbent material. In addition, thevessel may in some instances advantageously employ a heater operativelyarranged in relation to the storage and dispensing vessel for selectiveheating of the solid-phase physical sorbent medium, to effectthermally-enhanced desorption of at least a portion of the sorbate gasfrom the solid-phase physical sorbent medium. Since the storage anddelivery vessel of Tom et al. preferably operates in the sub-atmosphericregime, the pressure regulator assembly may be exteriorly located.

In the alternative, when higher storage pressures are required, thefluid is a liquid, or conditions warrant enhanced safety, at least onepressure regulator may be disposed at or within the vessel to retainfluid in the vessel, for example Advanced Technology Materials, Inc.(Danbury, Conn., USA) VAC™ cylinder (see, e.g., Wang, et al. U.S. Pat.No. 6,089,027, which is incorporated by reference herein in theentirety). Preferably, such elements are interiorly disposed to minimizethe possibility of impact and environmental exposure during use, and tominimize the leak path of the contained fluid from the vessel. When thepressure regulator is interiorly disposed, the vessel may utilize asingle weld or seam at the outlet port, to seal the vessel.

FIG. 1 is a schematic cross-portional, elevation view of the Wang et al.storage and gas dispensing system 10, which may be used to safely storegaseous or liquid hydride according to the present invention. The fluidstorage and gas dispensing system 10 includes a storage and dispensingvessel 12 including a cylindrical side wall 14, a bottom floor 16 and anupper neck portion 18, defining an enclosed interior volume 15 holdingthe gaseous hydride and adsorbent material 17. Illustrative gaseoushydrides include germane, stibine, silane, diborane, etc. When thehydride is a liquid, the storage and dispensing vessel 12 is devoid ofadsorbent material (the enclosed interior volume 15 of the vessel 12holds liquid hydride only).

Disposed in the upper neck portion 18 of the vessel 12 is a valve headassembly comprising valve 20 communicating with valve outlet 22, fromwhich vapor is dispensed from the vessel in the direction indicated byarrow A. The valve 20 is shown with an associated actuator 24, which maybe of any suitable type (electrical, pneumatic, etc.) as desired in thegiven end use application of the invention. Alternatively, the valve 20may be manually actuated, or provided with other flow control means.

The valve 20 is joined in gas flow communication with the pressureregulator 26, which is of a conventional type employing a poppet elementwhich may for example be spring biased in a closed condition and whereinthe poppet is subject to displacement when the pressure differentialacross the poppet element exceeds a certain level. The pressureregulator 26 may for example be set to a subatmospheric, atmospheric orsuperatmospheric pressure value. The specific pressure level is chosenwith respect to the fluid contained in the vessel, as appropriate to thestorage and dispensing operation.

Optionally, coupled with the pressure regulator 26 is a phase separator28, including a membrane element 30, which is permeable to gas or vapor,e.g., hydrogen, deriving from the decomposing fluid stored therein, butis impermeable to the fluid itself, e.g., gaseous hydride. Similarly,the Tom et al. vessel disclosed hereinabove may also optionally have aselective hydrogen membrane disclosed within the gas dispensingmechanism. Potential membrane compositions are described in more detailhereinafter.

When it is desired to dispense gas from the vessel 12, the valveactuator 24 is actuated to open valve 20, thereby permitting gas orvapor to flow through the permeable membrane 30, the pressure regulator26 and the valve 20, for egress from the valve head dispensing assemblythrough outlet 22. During gas dispensing, the fluid pressure regulatorwill maintain the pressure of the gas being dispensed at the set pointpressure level.

The regulator is a flow control device, which can be set at apredetermined pressure level to dispense gas or vapor from the cylinderat such pressure level. The pressure level set point may besuperatmospheric, subatmospheric or atmospheric pressure, depending onthe dispensing conditions, and the mode of gas discharge from thevessel. The storage and dispensing vessel described herein mayoptionally have check valves, which prevent the potentially dangeroussituation where air diffuses back into the vessel containing the gaseoushydride.

Like the Tom et al. vessel, dispensing of gases from the Wang et al.vessel may be effectuated by pressure differentials or selective heatingof the solid-phase physical sorbent medium to effect desorption of atleast a portion of the sorbate gas from the solid-phase physical sorbentmedium.

The storage and dispensing vessels of the Tom et al. and Wang et al.patents thus embody a substantial advance in the art, relative to theprior art use of high-pressure gas cylinders. Conventional high pressuregas cylinders are susceptible to leakage from damaged or malfunctioningregulator assemblies, as well as to rupture or other unwanted bulkrelease of gas from the cylinder if internal decomposition of the gasleads to rapid increasing interior gas pressure in the cylinder.

Hydride Decomposition

A recent discovery has demonstrated that silane gas (SiH₄), stored as anadsorbed-phase in a nano-composite medium at sub-atmospheric pressures,can self-decompose at a near constant rate, producing H₂ and solidsilicon. This decomposition occurs at room temperature without the needfor external heat or elevated pressure. This exciting, new hydrogenstorage concept involves, therefore, the release of hydrogen via thedecomposition of a gaseous hydride stored in a nano-composite,adsorbed-phase containing vessel according to the reaction:M_(x)H_(y)(g)→xM(s)+y/2H₂  (1)where M includes, but is not limited to, Si, Ge, Sb or B.

The thermodynamic tendency for this reaction to occur at roomtemperature is indicated by the Gibbs free energy of formation of thehydride at 298K, ΔG_(f), wherein the decomposition of certain hydridesis more thermodynamically favored than others. Stibine (SbH₃,ΔG°_(f)=+147.8 kJ/mole), germane (GeH₄, ΔG°_(f)=+113.4 kJ/mol), diborane(B₂H₆, ΔG°_(f)=+86.7 kJ/mol), and silane (SiH₄, ΔG°_(f)=+56.9 kJ/mole)are gaseous hydrides which, subject to kinetic limitations, canspontaneously decompose at room temperature. On the other hand, thedecomposition of methane (CH₄, ΔG°_(f)=−50.84 kJ/mol) is veryunfavorable under these conditions. Of these gases, silane stands out asthe leading candidate based on safety and abundance considerations.

Decomposition rates of the gaseous hydrides may be modulated by heatingthe vessel to increase kinetic decomposition rates, pressurizing thevessel to increase kinetic rates, using some of the generated hydrogento cool or heat up the vessel to slow down or accelerate hydrogengeneration, and/or modifying the surface sites of the adsorbent, e.g.,doping the carbon sorbent with phosphoric acid, to catalyzedecomposition, or boric acid, to suppress decomposition.

Suitable gaseous hydride materials generate hydrogen upon decomposition.Preferably, the by-products include a solid phase metal which isregenerable back to its gaseous hydride form. Optimum materials shouldform multiple hydrogen molecules for every parent gaseous hydride. Atthe same time, toxicity and reactivity of the gaseous hydride and itsby-products should be minimal. A final consideration for extensiveworld-wide use is availability. Materials suitable for use in the broadpractice of the invention include, silane, ammonia, boranes,hydrocarbons and other suitable Group IVA-VIA hydrides.

Silane can be adsorbed at ambient pressure on high capacity carbonmonoliths at a level of 140 g/L. Under conditions of stoichiometricdecomposition, the amount of silane necessary for 4.5% hydrogen storageis 286 g/L. The advantages offered by silane (e.g., it is a commoditychemical, less toxic than the other candidate compounds, and capable ofsafe delivery), far outweigh its disadvantages. Disilane or higher-ordersilanes can also be used. Suitable Group IVA-VIA hydrides include, butare not limited to ammonia (NH₃), germane (GeH₄), stibine (SbH₃), arsine(AsH₃), stanane (SnH₃), bismuth hydride (BiH₃), phosphine (PH₃),selenium hydride (SeH₂) and telerium hydride (TeH₂). Ammonia is lessreactive than silane and therefore may require a catalyst Advantageouslythough, the byproducts of the ammonia decomposition are nitrogen andhydrogen, which are easily separated. Boranes (diborane, pentaborane,decaborane) form elemental boron and hydrogen upon decomposition,whereby the boron metal that can be oxidized or re-hydrided.Hydrocarbons are less reactive than silanes and decompose to form carbonand hydrogen and the decomposition may require a catalyst and energyinput.

FIG. 2A illustrates an embodiment of the present invention based on theobservation that decomposition of the gaseous hydrides may be enhancedby surface modification, i.e., manipulating the carbon edge-siteconcentration, of the adsorbent material. Storage and dispensing vessel110, e.g., the Tom et al., the Wang et al., or variations thereof, issituated upstream of decomposition chamber 120. Situated between thevessel 110 and the decomposition chamber 120 are a series of valves 112,114, for example, pressure regulating valves, check valves, shut-offvalves, isolation valves, over-pressure relief valves, mass-flow controlvalves, etc. The valves 112, 114 may be manually or automaticallyactuatable. In addition, pressure switches and/or mechanical regulatorscan be used throughout the system to prevent backflow and to control thegeneration of hydrogen, thus ensuring safe operation of the system.

The decomposition chamber 120 is divided into at least two differentportions, a decomposition portion 122 and collection portion 124, saiddecomposition portion 122 and collection portion being bisected by a gasseparation membrane 126. The decomposition portion 122 has disposedtherein a quantity of surface modified adsorbent, e.g., H₃PO₄-dopedcarbon.

The gas separation membranes 126 used to perform the hydrogen/gaseoushydride separation are hydrogen-selective, that is, they permeatehydrogen preferentially over gaseous hydrides and all other gases in themix. The membrane used is a polymeric membrane based on molecular sizeor polarity and is selective for hydrogen over gaseous hydrides, whichcreates a gaseous hydride-depleted, hydrogen-enriched permeate stream.Representative references describing membrane separation processes suchas this include U.S. Pat. Nos. 4,362,613 and 4,367,135 to Monsanto, U.S.Pat. No. 4,548,619 to UOP, U.S. Pat. No. 5,053,067 to L'Air Liquide,U.S. Pat. No. 5,082,481 to Lummus Crest, U.S. Pat. No. 5,157,200 toInstitut Francais du Petrole, and U.S. Pat. No. 5,689,032 toKrause/Pasadyn. Polymers which may be suitable for the polymericmembranes and which may exhibit suitable selectivities for thepermeation of hydrogen as compared to the permeation of gaseoushydrides, can be substituted or unsubstituted polymers and for example,may be selected from polysulfones; poly(styrenes), includingstyrene-containing copolymers such as acrylonitrile-styrene copolymers,styrene-butadiene copolymers and styrene-vinylbenzylhalide copolymers;polycarbonates; cellulosic polymers, such as cellulose acetate,cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose,etc.; polyamides and polyimides, including aryl polyamides and arylpolyimides; polyethers, poly(arylene oxides) such as poly(phenyleneoxide) and poly(xylylene oxide); poly(esteramide-diisocyanate);polyurethanes; polyesters (including polyarylates), such aspoly(ethylene terephthalate), poly(alkyl methacrylates, poly(alkylacrylates), poly(phenylene terephthalate), etc.; polysulfides;poly(siloxanes); polymers from monomers having alpha-olefinicunsaturation other than mentioned above such as poly(ethylene),poly(propylene), poly(butene-1), poly(4-methyl pentene-1), polyvinyls,e.g., poly(vinyl chloride), poly(vinyl fluoride), poly(vinylidenechloride), poly(vinylidene fluoride), poly(vinyl alcohol), poly(vinylesters) such as poly(vinyl acetate) and poly(vinyl propionate),poly(vinyl pyridines), poly(vinyl pyrrolidones), poly(vinyl ethers),poly(vinyl ketones), poly(vinyl aldehydes) such as poly(vinyl formal)and poly(vinyl butyral), poly(vinyl amines), poly(vinyl phosphates), andpoly(vinyl sulfates); polyacetal; polyallyls; poly(benzobenzimidazole),polyhydrazides; polyoxadiazoles; polytriazoles; poly(benzimidazole);polycarbodiimides; polyphosphazinesl; etc., and interpolymers, includingblock interpolymers containing repeating units from the above, andgrafts and blends containing any of the foregoing. Typical substituentsproviding substituted polymers include halogens such as fluorine,chlorine and bromine; hydroxyl groups; lower alkyl groups; lower alkoxygroups; monocyclic aryl; lower acyl groups and the like. A preferred gasseparation membrane is Nafion®, which are a perfluorosulfonic acid/PTFEcopolymer in the acidic form.

In operation, desorption of the gaseous hydride stored in the storageand dispensing vessel 110 is effectuated by a pressure differential,i.e., the pressure downstream of the vessel is less than the pressurewithin the vessel, or alternatively, desorption is thermally-enhancedwhereby the vessel and/or the contents contained therein are heated by aheating means. The desorbed gaseous hydride from the storage anddispensing vessel 110 flows into the decomposition portion 122 of thedecomposition chamber 120, where decomposition of the hydride to formthe metal M and H₂ occurs.

The hydrogen gas generated during the decomposition reactionpreferentially passes through the gas separation membrane 126 to thecollection portion 124 of the decomposition chamber 120. Passage ofhydrogen gas from the decomposition portion 122 to the collectionportion 124 is effectuated by concentration and/or pressuredifferentials, which are well known in the membrane arts. When valve 130is open, hydrogen in the collection portion 124 of the decompositionchamber 120 passes through to the fuel cell 140. Optionally, thedecomposition chamber 120 may act as a holding chamber, wherein thehydrogen gas is stored in the collection portion 124 until apre-determined pressure threshold is reached. This serves to allowimmediate gas flow to the fuel cell on demand and to shorten the“waiting-period” associated with decomposition. The holding chamber mayfurther comprise flow-regulating devices, such as a mass flowcontroller, to achieve reproducible delivery of H₂ compounds into thefuel cell. A pump or venturi (not shown) may be disposed between thedecomposition chamber 120 and the storage and dispensing vessel 110and/or between the decomposition chamber 120 and the fuel cell 140 tofacilitate movement of gases from the vessel 110 to the decompositionchamber 120 and/or from the collection portion 124 to the fuel cell.

As previously introduced, one downside of many gas storage operations isthe continual decomposition of the silane or germane gas to hydrogen andsilicon/germanium during storage on non-doped sorbent materials, even atroom temperature. This detriment is advantageously addressed in thepractice of the present invention by using the spontaneous decompositionsystem described hereinabove as a hydrogen source. Towards that end, inyet another embodiment, the decomposition chamber 120 is devoid ofsurface modified adsorbent in the decomposition portion 122 (i.e., noadsorbent is present, or alternatively undoped adsorbent is present inthe decomposition portion). In this embodiment, the hydridespontaneously decomposes in the storage and dispensing vessel 110, thedecomposition portion 122 and/or the line connecting the two, and thehydrogen gas passes through the membrane as described in the previousembodiment For example, the decomposition of the gaseous hydride storedin the storage and dispensing vessel 110 may be modulated by adding orremoving energy to the vessel 110 (by heat, pressure, friction, etc)while valves 112 and/or 114 are closed. Hydrogen, to a large extent,would not be preferentially adsorbed onto the adsorbent media, and thusremains in the headspace of the vessel. Following the opening of valves112 and 114, the headspace gas is extracted out Any gaseous hydrideremoved together with the hydrogen gas can be separated from the gasstream using the gas separation membrane 126 or other chemical filter.Alternatively, the sorbent material contained in the storage anddispensing vessel 110 may include the surface modified adsorbent.

Another embodiment includes the positioning of a second holding chamberbetween the decomposition chamber and the fuel cell (not shown). In thisembodiment, the second holding chamber is separate from thedecomposition chamber 120 thereby ensuring that the concentration orpressure differential across the gas separation membrane 126 ismaximized. Optionally, a pump or a venturi (not shown) may be disposedbetween the decomposition chamber 120 and the fuel cell to facilitatemovement of hydrogen from the collection portion 124 to the secondholding chamber.

The storage and dispensing vessel 110, decomposition chamber 120 and thegas permeable membrane 126 may be of any size, shape and/orconfiguration depending on the circumstances and conditions of use,e.g., size of the fuel cell and the amount of hydrogen needed per unittime, as readily determined by one of skill in the art. The materialconstruction of the apparatus is also readily determined by one skilledin the art

In a particularly preferred embodiment, the storage and dispensingvessel is a light-weight, small volume, gas storage vessel rated toapproximately 50 psig containing silane at sub-ambient pressure, saidsilane being adsorbed onto a doped carbon sorbent, e.g., doped withphosphoric acid. The pressure of the adsorbed silane is preferablysub-atmospheric to minimize exposure of toxic silane to the user in theevent of an accidental release. The gas dispensing mechanism wouldincorporate a selective hydrogen separation membrane to preventdischarge of silane gas but allow hydrogen to egress from the vessel toa small, portable fuel cell. An individual, e.g., a soldier, carryingthe storage and dispensing vessel incorporated into a small fuel cellsystem would have electric power to continually charge a small batterysystem. Following complete discharge of the silane from the vessel, thevessel may be opened to the atmosphere allowing silicon oxidation toenvironmentally benign silica for proper disposal.

Material Regeneration:

Once the gaseous hydride has been fully utilized to generate hydrogen,the non-gaseous metal M remains in the decomposition portion 122 of thedecomposition chamber 120. In a further embodiment of the presentinvention, at least a portion of the metal M, e.g., Si, Ge, Sb and B,may be recycled back to the gaseous hydride form in order to completethe material lifecycle, i.e., “re-hydrided.” This is especiallyimportant when the storage and dispensing vessel 110 is of a volume thatis easily transportable, e.g., by humans or by automobile, but has alimited amount of gaseous hydride available for use.

Regeneration can be accomplished in situ or ex situ. Unlike currentreforming technologies used to generate hydrogen, which liberate thesecond element into the environment, e.g., carbon as a carbon oxide,this technology aims to confine the metal M for conversion back to agaseous hydride species. From a thermodynamic point of view, theenthalpy required for formation of the silane from Si and H₂ is +34.3kJ/mole while the heat of combustion of the generated hydrogen reaches−483.6 kJ, a net overall benefit of −449 kJ.

FIG. 2B illustrates an embodiment of the material regeneration inventionwherein at least a portion of the metal M remaining following thedecomposition reaction may be regenerated for reuse. As used herein,“re-hydrided” is defined as the regeneration of the metal M usinghydrogen gas to form stoichiometrically or non-stoichiometricallycomplete gaseous hydrides containing said metal. The storage anddispensing and decomposition components are numerically labeled the sameas in FIG. 2A. In FIG. 2B, a hydrogen-containing source 150 iscommunicatively connected to the collection portion 124 of thedecomposition chamber 120. Situated between the hydrogen-containingsource 150 and the decomposition chamber 120 are a series of valves 132,134, for example, pressure regulating valves, check valves, shut-offvalves, isolation valves, over-pressure relief valves, mass-flow controlvalves, etc. The valves 132, 134 may be manually or automaticallyactuatable. In addition, pressure switches and/or mechanical regulatorscan be used throughout the system to prevent backflow and to control thegeneration of hydrogen, thus ensuring safe operation of the system. Apump or venturi (not shown) may be disposed between the decompositionchamber 120 and the storage and dispensing vessel 110 and/or between thedecomposition chamber 120 and the hydrogen-containing vessel tofacilitate movement of gases from the source 150 to the decompositionchamber 120 and/or from the decomposition chamber 120 to the storage anddispensing vessel 110.

Notably, although the vessels, chambers and sources 110, 120 and 150 areschematically shown to be an equal volume, it should be appreciated thatthe size, shape and/or configuration of the individual vessels,chambers, sources and membranes may vary depending on the circumstancesand conditions of use, as readily determined by one skilled in the artFor example, the storage and dispensing vessel 110 may be of a size thatit is portable by humans, e.g., a foot soldier, however, thehydrogen-containing source 150 may be a vessel that is so large as to beutilized for regeneration purposes only. Alternatively, thehydrogen-containing source 150 is not a vessel per se, but represents aconventional hydrogen-generating system, e.g., water electrolysis usingelectricity, as known by those skilled in the art. In yet anotheralternative, the hydrogen-containing source 150 contains anotherhydride, e.g., a higher order hydride such as decaborane, which is ableto donate some of its hydrogen atoms to regenerate the leftover metal.As such, as defined herein “hydrogen-containing source” may be a vesselcontaining hydrogen in the form of hydrogen gas or a higher-orderhydride or a generating system that generates hydrogen gas.

In operation, hydrogen from the hydrogen-containing source 150 flowsinto the collection portion 124 of the decomposition chamber 120.Hydrogen entering the collection portion 124 passes through the gasseparation membrane 126 (as described hereinabove) to the decompositionportion 122 (which in this embodiment is a regeneration portion), wherethe hydrogen reacts with at least a portion of the metal M to form thegaseous hydride, according to the following reaction:xM(s)+y/2H₂(g)→M_(x)H_(y)(g)  (2)Thereafter, the gaseous hydride formed in the decomposition portion 122flows into the storage and dispensing vessel 110, where it adsorbs ontothe sorbent material contained therein. The time of regeneration isreadily determinable by one skilled in the art using known volumes, gasflows and the adsorption isotherm of the gaseous hydride onto thespecific sorbent material disposed within the storage and dispensingvessel 110 (see, e.g., FIG. 4, illustrating the adsorption of silaneonto various carbon sorbents). Following the required amount ofregeneration, the storage and dispensing vessel 110 is “full” of gaseoushydride and can be used to provide hydrogen to a fuel cell again. It isto be appreciated that a “full” storage and dispensing vessel does notnecessarily mean that the vessel is full in a theoretical sense, i.e.,based on the number of available adsorption sites, but rather no moregaseous hydride will adsorb onto the adsorbent material at the specificconditions of adsorption, i.e., pressure, temperature, etc.

In yet another alternative, a halogen gas is used to extract the metal Mcontained in the decomposition chamber 122 to generate metal halidesaccording to the reaction:xM(s)+y/2Cl₂→M_(x)Cl_(y)(g)  (2)Subsequently, the halogen atoms are displaced via reaction with hydrogengas (with heat, pressure, or catalysts) to form the hydride according tothe following reaction:M_(x)Cl_(y)(g)+y/2H₂(g)→M_(x)H_(y)(g)+y/2Cl₂(g)  (3)

During regeneration, heat and/or pressure may be used to facilitateconversion of at least a portion of the metal back to the gaseoushydride.

While the invention has been described herein with reference to variousspecific embodiments, it will be appreciated that the invention is notthus limited, and extends to and encompasses various other modificationsand embodiments, as will be appreciated by those ordinarily skilled inthe art. Accordingly, the invention is intended to be broadly construedand interpreted, in accordance with the ensuing claims.

1. An apparatus for storing and dispensing a sorbate gas, wherein thesorbate gas undergoes decomposition to form hydrogen gas, said apparatuscomprising: (a) a storage and dispensing vessel containing the sorbategas in a physically adsorbed state; and (b) a decomposition chamber,said decomposition chamber comprising a decomposition portion and acollection portion, wherein the storage and dispensing vessel iscommunicatively connected to the decomposition portion, and wherein thedecomposition portion and the collection portion are separated by a gaspermeable membrane.
 2. The apparatus of claim 1, wherein the storage anddispensing vessel comprises: (a) a vessel constructed and arranged forholding a solid-phase physical sorbent medium; (b) a solid-phasephysical sorbent medium disposed in said vessel at an interior gaspressure; (c) a sorbate gas physically adsorbed on said solid-phasephysical sorbent medium; and (d) a dispensing assembly coupled in gasflow communication with the vessel; wherein at least a portion of thesorbate gas desorbs from the solid-phase physical sorbent medium underdispensing conditions to yield desorbed sorbate gas for flow of saiddesorbed sorbate gas through the dispensing assembly.
 3. The apparatusof claim 1, wherein the sorbate gas comprises a gaseous hydride.
 4. Theapparatus of claim 3, wherein the gaseous hydride comprises a hydrideselected from the group consisting of silane, germane, stibine anddiborane.
 5. The apparatus of claim 3, wherein the gaseous hydridecomprises silane.
 6. The apparatus of claim 2, wherein the solid-phasephysical sorbent medium disposed in said vessel comprises a materialselected from the group consisting of silica, carbon molecular sieves,alumina, macroreticulate polymers, kieselguhr, carbon, andaluminosilicates.
 7. The apparatus of claim 1, wherein the gas permeablemembrane is selective for hydrogen over the sorbate gas.
 8. Theapparatus of claim 1, wherein the gas permeable membrane comprisesperfluorosulfonic acid.
 9. The apparatus of claim 1, further comprisinga modified surface adsorbent in the decomposition portion of thedecomposition chamber.
 10. The apparatus of claim 9, wherein themodified surface adsorbent comprises a phosphoric acid doped carbonadsorbent.
 11. The apparatus of claim 9, wherein the modified surfaceadsorbent comprises a boric acid doped carbon adsorbent.
 12. Theapparatus of claim 1, further comprising a fuel cell communicativelyconnected to the collection portion of the decomposition chamber,wherein the fuel cell is positioned downstream of the collection portionof the decomposition chamber.
 13. The apparatus of claim 1, wherein thegas sorbate decomposes in the storage and dispensing vessel.
 14. Theapparatus of claim 1, wherein the gas sorbate decomposes in thedecomposition portion of the decomposition chamber.
 15. The apparatus ofclaim 2, wherein the dispensing assembly comprises at least one gasregulator positioned between the storage and dispensing vessel and thedecomposition chamber.
 16. The apparatus of claim 2, wherein thedispensing assembly comprises at least one gas regulator disposed withinthe vessel.
 17. The apparatus of claim 2, wherein the interior gaspressure is subatmospheric.
 18. The apparatus of claim 2, wherein theinterior gas pressure is atmospheric.
 19. The apparatus of claim 2,further comprising a heater operatively arranged in relation to thevessel for selective heating of the solid-phase physical sorbent medium,to effect thermally-enhanced desorption of at least a portion of thesorbate gas from the solid-phase physical sorbent medium.
 20. Theapparatus of claim 2, wherein the vessel is constructed and arranged toeffect desorption of at least a portion of said sorbate gas from thesolid-phase physical sorbent medium under dispensing conditionsincluding a pressure exterior of said vessel below said interiorpressure.
 21. The apparatus of claim 2, wherein the solid-phase physicalsorbent medium comprises a modified surface adsorbent.
 22. The apparatusof claim 21, wherein the modified surface adsorbent comprises aphosphoric acid doped carbon adsorbent or a boric acid doped carbonadsorbent.
 23. The apparatus of claim 1, wherein the sorbate gasdecomposes at room temperature.
 24. The apparatus of claim 3, whereinthe gaseous hydride generates hydrogen gas and metal upon decomposition.25. The apparatus of claim 24, wherein the metal comprises a speciesselected from the group consisting of silicon, germanium, boron andantimony.
 26. The apparatus of claim 24, wherein the metal is at leastpartially regeneratable to the gaseous hydride.
 27. The apparatus ofclaim 1, further comprising a hydrogen-containing source communicativelyconnected to the collection portion of the decomposition chamber.
 28. Anapparatus for storing, dispensing and regenerating a sorbate gas, saidapparatus comprising: (a) a storage and dispensing vessel containing thesorbate gas in a physically adsorbed state; (b) a decomposition chamber,said decomposition chamber comprising a decomposition portion and acollection portion separated by a gas permeable membrane, saiddecomposition portion having a modified surface adsorbent disposedtherein, wherein the storage and dispensing vessel is communicativelyconnected to the decomposition portion of the decomposition chamber, andwherein the sorbate gas undergoes decomposition in the decompositionchamber to form a metal and hydrogen gas therein; and (c) ahydrogen-containing source communicatively connected to the collectionportion of the decomposition chamber.
 29. The apparatus of claim 28,wherein the hydrogen-containing source supplies hydrogen to thedecomposition chamber to re-hydride at least a portion of the metalcontained therein.
 30. The apparatus of claim 29, wherein the modifiedsurface adsorbent comprises a phosphoric acid doped carbon adsorbent ora boric acid doped carbon adsorbent.
 31. The apparatus of claim 28,wherein the sorbate gas comprises a gaseous hydride.
 32. The apparatusof claim 31, wherein the gaseous hydride comprises a species selectedfrom the group consisting of silane, germane, stibine and diborane. 33.The apparatus of claim 28, wherein the gas permeable membrane isselective for hydrogen over the sorbate gas.
 34. The apparatus of claim28, wherein the gas permeable membrane comprises perfluorosulfonic acid.35. The apparatus of claim 28, wherein the sorbate gas decomposes atroom temperature.
 36. An apparatus for storing and dispensing a sorbategas, said apparatus comprising a storage and dispensing vesselcontaining the sorbate gas, said storage and dispensing vesselcomprising: (a) a vessel constructed and arranged for holding asolid-phase physical sorbent medium; (b) a solid-phase physical sorbentmedium disposed in said vessel at an interior gas pressure; (c) asorbate gas physically adsorbed on said solid-phase physical sorbentmedium; and (d) a dispensing assembly coupled in gas flow communicationwith the vessel and selectively actuatable for gas dispensing, whereinthe dispensing assembly comprises a gas permeable membrane within thevessel, wherein at least a portion of the sorbate gas undergoesdecomposition in the vessel to form hydrogen gas, and hydrogen gasegresses the vessel through the gas permeable membrane of the dispensingassembly during said gas dispensing.
 37. The apparatus of claim 36,wherein the sorbate gas comprises a gaseous hydride.
 38. The apparatusof claim 37, wherein the gaseous hydride comprises a species selectedfrom the group consisting of silane, germane, stibine and diborane. 39.The apparatus of claim 36, wherein the solid-phase physical sorbentmedium disposed in said vessel comprises a material selected from thegroup consisting of silica, carbon molecular sieves, alumina,macroreticulate polymers, kieselguhr, carbon, and aluminosilicates. 40.The apparatus of claim 36, wherein the solid-phase physical sorbentmedium comprises a modified surface adsorbent.
 41. The apparatus ofclaim 40, wherein the modified surface adsorbent comprises a phosphoricacid doped carbon adsorbent or a boric acid doped carbon adsorbent. 42.The apparatus of claim 36, wherein the gas permeable membrane isselective for hydrogen over the sorbate gas.
 43. The apparatus of claim36, wherein the gas permeable membrane comprises perfluorosulfonic acid.44. The apparatus of claim 36, further comprising a fuel cellcommunicatively connected downstream of the storage and dispensingvessel.
 45. The apparatus of claim 36, wherein the dispensing assemblycomprises at least one gas regulator disposed within the vessel.
 46. Theapparatus of claim 36, wherein the interior gas pressure issubatmospheric.
 47. The apparatus of claim 36, wherein the interior gaspressure is atmospheric.
 48. The apparatus of claim 36, wherein thevessel is constructed and arranged to effect desorption of at least aportion of said sorbate gas from the solid-phase physical sorbent mediumunder dispensing conditions including a pressure exterior of said vesselbelow said interior pressure.
 49. The apparatus of claim 36, wherein thesorbate gas decomposes at room temperature.
 50. A method for generatinghydrogen gas by the decomposition of a sorbate gas, said methodcomprising: (a) desorbing at least a portion of said sorbate gas from asolid-phase physical sorbent medium disposed in a storage and dispensingvessel, said storage and dispensing vessel comprising a solid-phasephysical sorbent medium having a physically sorptive affinity for saidsorbate gas disposed therein; (b) flowing the sorbate gas from thestorage and dispensing vessel to a decomposition chamber; and (c)decomposing the sorbate gas in the decomposition chamber to generatehydrogen gas.
 51. The method of claim 50, wherein the sorbate gas isdesorbed from the solid-phase physical sorbent medium by reducedpressure desorption.
 52. The method of claim 50, wherein the sorbate gasis desorbed from the solid-phase physical sorbent medium bythermally-enhanced desorption.
 53. The method of claim 50, wherein thesorbate gas comprises a gaseous hydride.
 54. The method of claim 53,wherein the gaseous hydride comprises a species selected from the groupconsisting of silane, germane, stibine and diborane.
 55. The method ofclaim 53, wherein the gaseous hydride comprises silane.
 56. The methodof claim 50, wherein the solid-phase physical sorbent medium comprises amaterial selected from the group consisting of silica, carbon molecularsieves, alumina, macroreticulate polymers, kieselguhr, carbon, andaluminosilicates.
 57. The method of claim 50, wherein the solid-phasephysical sorbent medium comprises a modified surface adsorbent.
 58. Themethod of claim 57, wherein the modified surface adsorbent comprises aphosphoric acid doped carbon adsorbent or a boric acid doped carbonadsorbent.
 59. The method of claim 50, wherein the decomposition chambercomprises a decomposition portion and a collection portion which areseparated by a gas permeable membrane.
 60. The method of claim 59,wherein the gas permeable membrane is selective for hydrogen over thesorbate gas.
 61. The method of claim 59, wherein the gas permeablemembrane comprises perfluorosulfonic acid.
 62. The method of claim 59,further comprising flowing the hydrogen gas into a fuel cell that iscommunicatively connected to the collection portion of the decompositionchamber.
 63. The method of claim 50, wherein the storage and dispensingvessel comprises a dispensing assembly.
 64. The method of claim 63,wherein the dispensing assembly comprises at least one gas regulatorpositioned between the storage and dispensing vessel and thedecomposition chamber.
 65. The method of claim 63, wherein thedispensing assembly comprises at least one gas regulator disposed withinthe storage and dispensing vessel.
 66. The method of claim 50, whereinthe sorbate gas decomposes at room temperature.
 67. The method of claim53, wherein the gaseous hydride generates hydrogen gas and metal upondecomposition.
 68. The method of claim 67, further comprisingregenerating the metal by introducing hydrogen from ahydrogen-containing source to the decomposition chamber to re-hydridethe metal.
 69. The method of claim 50, further comprising flowing thehydrogen gas to a fuel cell.
 70. The method of claim 50, wherein thesolid-phase physical sorbent medium has physically sorptive affinity forsaid sorbate gas disposed therein.
 71. The method of claim 50, whereinthe gas sorbate decomposes in the storage and dispensing vessel.
 72. Themethod of claim 59, wherein the gas sorbate decomposes in thedecomposition portion of the decomposition chamber.
 73. A method forgenerating hydrogen gas by the decomposition of a sorbate gas, saidmethod comprising: (a) physically adsorbing a sorbate gas into asolid-phase physical sorbent medium having sorptive affinity for saidsorbate gas, wherein the solid-phase physical sorbent medium is disposedin a storage and dispensing vessel comprising a dispensing assembly; (b)decomposing at least a portion of said sorbate gas physically adsorbedinto the solid-phase physical sorbent medium to form hydrogen; and (c)flowing the hydrogen gas from the storage and dispensing vessel to ahydrogen gas consuming unit.
 74. The method of claim 73, wherein thedispensing assembly of the storage and dispensing vessel includes a gaspermeable membrane to separate the sorbate gas from hydrogen gas. 75.The method of claim 73, wherein the sorbate gas comprises a gaseoushydride.
 76. The method of claim 75, wherein the gaseous hydridecomprises a species selected from the group consisting of silane,germane, stibine and diborane.
 77. The method of claim 73, wherein thesolid-phase physical sorbent medium disposed in said vessel comprises amaterial selected from the group consisting of silica, carbon molecularsieves, alumina, macroreticulate polymers, kieselguhr, carbon, andaluminosilicates.
 78. The method of claim 73, wherein the solid-phasephysical sorbent medium comprises a modified surface adsorbent.
 79. Themethod of claim 78, wherein the modified surface adsorbent comprises aphosphoric acid doped carbon adsorbent or a boric acid doped carbonadsorbent.
 80. The method of claim 74, wherein the gas permeablemembrane is selective for hydrogen over the sorbate gas.
 81. The methodof claim 74, wherein the gas permeable membrane comprisesperfluorosulfonic acid.
 82. The method of claim 74, wherein the hydrogengas consuming unit comprises a fuel cell.
 83. The apparatus of claim 74,wherein the sorbate gas decomposes at room temperature.